Limit switch motor braking control for hoists



Sept. 1, 1964 D. E. CHILDS. 3,147,421

LIMIT swrrcn MOTOR BRAKING cou'rRoL FOR HOISTS Filed Nov. 13, 1961 \5 gI \9 HOISTFLOWER 1/ LII-l XVR as I m F/g.

2 INVENTOR.

DAVID e. CHILDS ATTORNEY United States Patent Ohio Filed Nov. 13, 1961,Ser. No. 151,850 8 Claims. (Cl. 318-266) This invention relates toelectric control systems and more particularly to a system forcontrolling an electric motor when used to hoist and lower a load.

Heretofore, electric control systems of this type did not rapidly stopand hold the load after it was hoisted through the overhoist limitswitch when the drum controller was left in one of the hoist positions.The contacts of the overhoist limit switch, when tripped, disconnect themotor from the source of power and reconnect it in a dynamic brakingcircuit to assist in stopping the upward movement of the load. Once thisupward movement is stopped, the load was allowed to lower out of theoverhoist limit switch due to its own weight and because the overhoistlimit switch contacts did not disconnect the winding of the frictionbrake from the source of power. As soon as the load lowered out of theoverhoist limit switch, the overhoist limit switch reset and itscontacts operated to reconnect the motor to the source; and since thedrum controller remained in one of the hoist positions, the load wouldagain hoist through the overhoist limit switch. This cycling of the loadin and out of the overhoist limit switch was dangerous and, in addition,caused undue wear on the equipment.

It is therefore an object of this invention to provide a hoist controlsystem which prevents the cycling of the load through the overhoistlimit switch.

It is another object of this invention to provide a hoist control systemwith a protective system that is more sensitive to the operation of themotor in the hoist direction after going through the overhoist limitswitch than it is to the operation of the motor in the other conditions.

It is another object of this invention to provide a hoist system whichprevents the speed of lowering out of the overhoist limit switch frombecoming excessive.

It is still another object of this invention to prevent the motor fromrunning away should the overhoist limit switch fail to reset during thelowering of the load through it.

The embodiment of this invention utilizes a voltage relay that isconnected to be energized by the voltage drop across the series fieldwinding when the overhoist limit switch is in its normal untrippedcondition, and that is connected to be energized by the voltage dropacross the dynamic braking resistor when the overhoist limit switch istripped. The voltage relay has contacts in the hoist control circuit andwhen it is operated, it causes the motor and brake to be disconnectedfrom the source of power whereby the brake sets to stop and hold theload.

The voltage relay is polarized in that it is operated by a lower voltageafter the tripping of the overhoist limit switch due to a load beinghoisted therethrough than the voltage required to operate the relayunder the other operating conditions of hoisting and lowering. This isvery desirable and increases the stability of the hoist operationbecause it allows the voltage to operate the relay 3,147,42l PatentedSept. 1, 1964 after the overhoist limit switch has been tripped to bevery small, and it is in this instance, that it is desirable to have therelay operate as soon as possible. In the other operating condition, therelay is required to operate only when excessive conditions exist, andunder these conditions a much larger voltage signal is present. Also,aids in reducing the possibility of relay operation due to transients.

It is also desirable to utilize a relay which has a slight time delaybetween its energization and the operation of its contacts as isdescribed in the co-pending application of Harry M. Cook and ChristianChermely, filed on or about July 10, 1961, bearing Serial Number122,817, and having the same assignee as the instant application.

Operation of the relay requires that the control circuit be reset bymoving the drum controller to the OH position and thereby re-establishthe energizing circuit for the control circuit.

Other objects and advantages of this invention will become apparent tothose skilled in the art when the following description is read inconjunction with the drawings in which:

FIGURE 1 is an across-the-line type of diagram of the power and controlcircuits for a hoist system; and

FIGURE 2 is another embodiment of this invention illustrating the methodof connecting the relay.

Referring to the drawings, there is shown at it) in FIG- URE 1 anarmature of a DC. motor having a series field winding 11.

Armature 10 is connected to be energized from a source of DC. powerrepresented by lines 12 and 13 through contacts of various contactors.When contactors M and H are operated to close contacts M1 and H1,armature It is energized to rotate in the hoisting direction. Whencontactors M and L are operated to close contacts M1 and L1, armature 10is energized to rotate in the lowering direction.

Armature 10 is connected by a drive shaft 14 to a hoist drum 15 whichhas a cable 16 wound thereon. At the free end of cable 16 is a load hook17 which serves as the means of engaging the load to be hoisted orlowered. Hook 17 has an arm 18 which serves to engage and operate anoverhoist limit switch when hook 1'7 is hoisted too high. The overhoistlimit switch is diagrammatically represented at 19 and has normally opencontacts 20 and 21 and normally closed contacts 22 and 23.

Armature 1th is also connected to a normally set friction brake (notshown) of known construction, having an electromagnetic winding 24 forreleasing the friction brake when energized. When winding 24 is notenergized, the friction brake sets to stop rotation of armature 10 anddrum 15.

At 25 generally is a drum type controller which, in the diagrammaticillustration thereof, comprises movable con tacts 26 to 36. Contacts 27through 36 are all connected together as shown and connected to contactUVl and wire 37 to wire 12. Contact 26 is connected directly to wire 37to wire 12 and will only conduct current when drum controller 25 is inits off position.

These contacts, as will be understood by those skilled in the art, areall movable in unison from the illustrated off position towards theright to five successive lowering points, La to Le, or towards the leftto five successive hoisting points, Ha to He, indicated by the verticallines below the legends Lowering and Hoisting.

On the several lowering points, movable contacts 27 and 28 and 311 to 36are engageable with bar contacts 38 to 46; and on the several hoistingpoints, movable contacts 27 to 29 and 32 to 36 are engageable with barcontacts 47 to 54.

Drum controller 25, on the various described points, operates orrestores electromagnetic contactors as follows.

A contactor UV having a winding 55 and normally open contacts UV1 andUV2.

A contactor M having a winding 56 and a normally open contact M1.

A contactor A having a winding 57 and a normally open contact 5A1 and anormally closed contact 5A2.

A contactor H having a winding 58 and normally open contacts H1 and H2and a normally closed contact H3.

A contactor L having a winding 59 and normally open contacts L1 and L2and a normally closed contact L3.

A contactor 1A having a winding 60 and a normally open contact 1A1 and anormally closed contact 1A2.

A contactor S having a winding 61 and normally open contacts S1 to S3and a normally closed contact S4.

A contactor CR having a winding 62 and a normally open contact CR1 andnormally closed contacts CR2 and CR3.

A contactor DB having a winding 63 and a normally open contact DB1 andnormally closed contacts DB2 and DB3.

A contactor 2A having a winding 64 and normally open contacts 2A1 and2A2 and a normally closed contact 2A3.

A timing contactor 2T having a winding 65 and a normally closed contact2T1.

A timing contactor 1T having a winding 66 and a normally open contact1T1 and a normally closed contact 1T2.

A timing contactor 3T having a winding 67 and normally open contacts 3T1and 3T2.

A contactor 3A having a winding 68 and normally open contacts 3A1 and3A2 and a normally closed contact 3A3.

A contactor 4A having a winding 69 and normally open contacts 4A1 and4A2 and a normally closed contact 4A3.

Timing contactors 1T, 2T and ST are of the known type that have meansdelaying their contact operation until a time interval has elapsed afterthe energization of their windings.

The contactors and timing contactors are all illustrated in normallyde-energized or restored condition. The said contacts of thesecontactors and timing contactors are shown without connection thereto,but are reproduced elsewhere in the drawing, with their connections, tothere'- by avoid the complexity in the drawings.

The windings of the contactors are shown in an acrossthe-line type ofdiagram comprising horizontal lines 70 to 80, with their left endsconnected to the various bar contacts of drum controller 25. The rightend of wire 70 is connected to wire 13. The right end of wires 71 to 76are connected to a wire 81. The right end of wires 77 to 36 areconnected to a wire 82.

In the illustrated 01f position of drum controller 25, contactor UV isoperated by current through controller contact 26, cross Wire 70,winding 55 of contactor UV and contact XVR1 to wire 13. Contactor UVoperates to close contact UV1 which connects wire 12 via wire 37directly to contacts 27 through 36. Contact UV2 closes to connect wire81 to wire 13. The control circuit is now connected to the source ofpower and ready for operation.

On the first point of hoisting Ha, contactor M is operated by currentthrough contact 27, bar contact 47, cross wire 71, winding 56, wire 81and contact UV2 to wire 13. Contactor M operates to close contact M1.

At the same time, contactor H is operated by current from contact 29,through bar contact 49, cross wire 73, contact S4, winding 58 ofcontactor H, wire 81 and contact UV2 to wire 13. Contactor H operates toclose contacts H1 and H2 and open contact H3.

The operation of contactors M and H connect the motor so that it isenergized by current flowing from wire 12 through contact H1, contact22, armature 10, contact 23, series field 11, winding 24, resistorsections R1, R2, R3 and R4, and contact M1 to wire 13. Resistor sectionsR5 and R6 and contact DB2 are connected in parallel with contact 22,armature 10, contact 23 and series field 11.

The current flowing through winding 24 of the friction brake releasesthe brake, allowing the motor to rotate. Armature 10 is energized withcurrent in a direction to cause the motor to rotate in the hoistingdirection, but at a low hoisting speed due to the series connectedresistors R1 to R4 and the armature shunt circuit of resistors R5 andR6.

On going to the second point of hoisting Hb, the operating conditionsdescribed for the first point hoisting remain the same; andadditionally, contactor 5A operates to short out resistance section R2and contactor DB operates to open the armature shunt circuit as follows.

Current flows through controller contact 28, bar contact 48, cross wire72, contact 2T2, winding 57 of contactor 5A, wire 81 and contact UV2 towire 13. Contactor 5A opeartes to close contact 5A1 which shorts outresistance section R2, and contact 5A2 opens.

Controller contact 32 engages with bar contact 50 and current flowstherethrough and through contact H2, cross wire 76, winding 63 ofcontactor DB, contact DB3, wire 81 and contact UV2 to wire 13. ContactorDB operates to close contact DB1 and open contacts DB2 and DB3. Theopening of contact DB2 disconnects the armature shunt circuit consistingof resistors R5 and R6. The opening of contact DB3 inserts resistor R7in the energizing circuit of winding 63. The closing of contact DB1connects wire 82 to wire 13.

The motor is now energized by current from wire 12 through contact H1,contact 22, armature 10, contact 23, series field 11, winding 24,resistor R1, resistor R3, resistor R4- and contact M to wire 13.Armature It is now energized with a higher current and is caused tohoist the load at a faster speed.

On going to the third point of hoisting He, the operating conditionsdescribed for the second hoisting point remain the same; andadditionally, contactor A2 operates to connect resistors R8, R9 and R10in parallel with resistors R1 and R3 which is accomplished as follows.

Controller contact 33 engages with bar contact 51 and current flowstherethrough and through cross wire 77, contact L3, winding 64 ofcontactor 2A, wire 82 and contact DB1 to wire 13. Contactor 2A operatesto close contacts 2A1 and 2A2 and open contact 2A3. The closing ofcontact 2A1 connects resistors R8, R9 and R10 in parallel with resistorsR1 and R3.

The closing of contact 2A2 allows current to flow from controllercontact 34 through bar contact 52, contact 2A2, cross wire 78, winding66 of timing contactor 1T, wire 82 and contact DB1 to wire 13. After theelapse of a time interval, contactor 1T operates to close contact 1T1and open contact 1T2.

The motor is now energized by current from wire 12 through contact H1,contact 22, armature 10, contact 23, series field 11, winding 24, theparallel connected resistors R1 and R3, and R8, R9 and R10, resistor R4,and contact M1 to wire 13. The armature is now eners gized withincreased currents so the motor hoist the load at a higher speed.

On going to the fourth point of hoisting Hd, the operating conditionsdescribed for the third hoisting point remain the same; andadditionally, contactor 3A operates to short out resistor R10 andconnects resistors operates to i R1, R3 and R4 in parallel wtihresistors R8 and R9 as follows.

Controller contact 35 engages with bar contact 53 and current flowstherethrough and through cross wire 79, contact 1A2, contact 1T1,winding 68 of contactor 3A, wire 82 and contact DB1 to wire 13. It is tobe noted, that winding 68 cannot be energized until after the expirationof the time interval of timing contactor 1T. After this expires,contactor 3A is operated to close contacts 3A1 and 3A2 and open contact3A3. The closing of contact 3A1 shorts out resistor R10 to connectresistor R1, R3 and R4 in parallel with resistors R8 and R9.

The closing of contact 3A2 allows winding 67 of timing contactor 3T tobe energized through the circuit consisting of controller contact 34,bar contact 52, cross wire 78, contact 3A2, winding 67, wire 82 andcontact DB1 to wire 13. After the expiration of its time interval,contacts 3T1 and 3T2 operate to close.

Current now flows through the motor from wire 12 to contact H1, contact22, armature 10, contact 23, series field 11, winding 24, the parallelcircuit of resistors R1, R3, R4 and contact M1, and resistors R8 and R9to wire 13. The motor is energized with a still higher current to causeit to hoist the load faster.

On going to the fifth point of hoisting He, the operating conditionsdescribed for the fourth hoisting point remain the same; andadditionally, contactor 4A operates to remove all of the resistance fromthe armature circuit as follows.

Controller contact 36 engages with bar contact 54 and current flowstherethrough and through cross wire 80, contact 3T2, winding 69 ofcontactor 4A, wire 82 and contact DB1 to wire 13. Contactor 4A cannotoperate until after the elapse of the time interval for timing contactor3T, after the expiration of which, contactor 4A operates to closecontacts 4A1 and 4A2 and open contact 4A3. The closing of contact 4A1shorts out all the remainder resistor sections from the motor circuit.

The motor is now energized by current flowing from wire 12 throughcontact H1, contact 22, armature 10, contact 23, series field 11,winding 24, contact 2A1 and contact 4A1 to wire 13. The motor is nowenergized with its maximum current and will therefore hoist the load atthe maximum speed.

On going to the first point of lowering La, contactors M, L and 5A areoperated as follows.

Controller contact 27 engages with bar contact 38 and current flowstherethrough and through cross wire 71, winding 56 of contactor M, wire81 and contact UV2 to wire 13. Contactor M operates to close contact M1.

Controller contact 28 engages with bar contact 39 and current flowstherethrough and through cross wire 72, contact 2T1, winding 57 ofcontactor 5A, wire 81 and contact'UV2 to wire 13. Contactor 5A operatesto close contact 5A1 and open contact 5A2.

Controller contact 30 engages with bar contact 40 and current flowstherethrough and through cross wire 74, contact 2A3, winding 59 ofcontactor L, wire 81 and contact UV2 to wire 13. Contactor L operates toclose contacts L1 and L2 and open contact L3.

Also, current flows from controller contact 30 through bar contact 40,cross wire 74, contact 2A3, contact 1T2, winding 60 of contactor 1A,wire 81 and contact UV2 to wire 13. Contactor 1A operates to closecontact 1A1 and open contact 1A2.

The motor is now connected to be energized as a shunt motor by currentflowing from wire 12 through contact L1, the circuit of armature 10,contact 22, resistors R5 and R6, and contact DB2, connected in parallelwith contact 23 and series field 11, and thence through winding 24 andresistor R1, and parallel connected resistor R3 with resistors R9 andR10, resistor R4 and contact M1 to wire 13.

On going to the second point of lowering Lb, the operating conditionsdescribed for the first lowering point remain the same; andadditionally, contactors S and DB are energized to continue to operatethe motor as a shunt motor as follows.

Controller contact 31 engages bar contact 41 and current flowstherethrough and through cross wire 75, contact H3, winding 61 ofcontactor S, wire 81 and contact UV2 to wire 13. Contactor S operates toclose contacts S1 to S3 and open contact S4.

Controller contact 32 engages with bar contact 42 and after contact S2closes, current flows from contact 32 through bar contact 42, contactS2, cross wire 76, winding 63 of contactor DB, contact DB3, wire 81 andcontact UV2 to wire 13. Contactor DB operates to close contact DB1 andopen contacts DB2 and DB3. Even though contact DB3 opens, winding 63 ismaintained energized through resistor R7.

Current now flows through to energize the motor from wire 12 throughcontact L, the circuit of armature 10, contact 22, resistor R5, contactS1 and resistor R8, all connected in parallel with the circuit ofcontact 23, series field 11, winding 24, resistor R1 and contact 1A1,and thence through resistors R9 and R18 connected in parallel withresistor R3, and through resistor R4 and contact M1 to wire 13.. Thisincreases the current flowing through armature 10 to increase this motorspeed so it lowers the load faster.

On going to the third point of lowering Lc, the operating conditionsdescribed for the second lowering point remain the same, except thatcontactors 3A, 4A, and CR and timing contactors IT and ST becomeenergized and contactor 1A becomes tie-energized.

Controller contact 34 engages bar contact 44 and current flowstherethrough and through contact L2, cross wire 78, winding 66 of timingcontactor 1T, wire 82 and contact DB1 to wire 13. After the expirationof its time interval, timing contactor 1T operates to close contact 1Tand open contact 1T2. The opening of contact 1T2 de-energizes winding 60and contactor 1A restores to open contact 1A1 and close contact 1A2.

The closing of contacts 1A2 and 1T1 allows current to flow fromcontroller contact 35 through bar contact 45, cross wire 79, contact1A2, contact 1T1, winding 68 of contactor 3A, wire 82, and contact DB1to wire 13. Contactor 3A operates to close contacts 3A1 and 3A2 and toopen contact 3A3.

The closing of contact 3A2 allows current to flow from controllercontact 34, through bar contact 44, contact 3A2, winding 67 of timingcontactor 3T, wire 82, and cont-act DB1 to wire 13. After the expirationof its time interval, timing contactor 3T operates to close its contacts3T1 and 3T2.

The closing of contact 3T2 allows current to flow from controllercontact 36, through ba-r contact 46, cross wire 88, contact 3T2, winding69 of contactor 4A, wire 82 and contact DB1 to wire 13. Contactor 4Aoperates to close contacts 4A1 and 4A2 and to open contact 4A3.

The closing of contact 4A2 allows current to flow from controllercontact 31, through bar contact 41, cross wire 75, contact H3, contact4A2, winding 62 of contactor CR, wire 81 and contact UV2 to wire 13.Contractor CR is operated to close contact CR1 and open contacts SR2 andCR3.

Current now flows to energize the motor from wire 12 through contact L1and the circuit of armature 10, contact 22, resistor R5, contact S1,contact 4A1 to wire 13 which is connected in parallel with the circuitof contact 23, series field 11, Winding 24, resistors R1, R3 and R4,

and contact M1 to wire 13. This increases the current allowed to flowthrough armature 10 to still further increase the motor speed and allowsthe lowering speed of the load to be increased.

On going to the fourth point of lowering Ld, the operating conditionsdescribed for the third lowering point remain the same, eXcept thatcontactors M and 3A become de energized as follows.

vWinding 46 becomes de-energized and contactor M restores whencontroller contact 27 leaves bar contact 38. Winding 68 becomestie-energized and contactor 3A restores when controller contact 35leaves bar contact 45.

Current now flows through to energize the motor from wire 12 throughcontact L1, the circuit of armature 16, contact 22, resistor R5, contactS1 and the parallel cirquit of contact 23, series field 11, winding 24,resistors R1, R3, R10, R9 and R8, and thence through contact 4A1 to wire13. This further increases the current through armature 10 to increasethe speed at which the motor drives the load downward.

On going to the fifth point of lowering Le, the operating conditionsdescribed for the fourth lowering point remain the same, except thatcontactor 5A is de-energized as follows. 7

Controller contact 33 engages with bar contact 43 and current flowstherethrough and through cross wire 77, contact CR1, winding 65 oftiming contactor 2T, wire 82 and contact DB1 to wire 13. After theelapse of its time interval, timing contacto-r 2T operates to open itscontact 2T1.

The opening of contact 2T1 opens the circuit energizing winding 57 andit becomes de-energized to restore contactor 5A which opens contact 5A1and closes contact 5A2. Current now flows toenergize the motor from wire12 through contact L1, the circuit of armature 10, contact 22, resistorR5, contact S1 and the parallel connected circuit of contact 23, seriesfield 11, winding 24, resistors R1 R2, R3, R4, R10, R9 and R8, andthence through contact 4A1 to wire 13. This increases the currentflowing through armature 10 to its maximum whereby the lowering speed ofthe load is increased to its maximum. 7 A

When hook 17 is hoisted too high, arm 18 engages overhoist limit switch19 causing contacts 22 and 23 to open and contacts 20 and 21 to close.

The openings of contacts 22 and 23 disconnect armature 10 and seriesfield 11 from the source of power. It also interrupts the power to brakewinding 24 unless drum controller 25 is in the first point hoisting, Ha.The closing of contacts 20 and 21 reconnect armature 16 and series field11 in a dynamic braking circuit which has connected in series a dynamicbraking resistor R11. Current now flows from armature 10 through contact21, series field 11, resistor R11, contact 20 back to armature 10. Thisflow of current produces dynamic braking torque and will assist inrapidly stopping the motor.

V, Relay XVR has two windings 83A and 83B wound in the same direction ohits core. Bothv windings are connected in parallel with resistor R11when contact 20 is closed. Winding 83 has a rectifier 85 connected inseries with it in a manner to permit the flow of the current throughwinding 83A only after overhoist limit switch 19 has been tripped and adynamic braking current is flowing. Therefore, after overhoist limitswitch 19 has been tripped both windings 83A and 83B will be energizedby the voltage drop across resistor R11 to operate relay XVR.

When relay XVR is operated, it opens its contacts XVR1. Contact XVR1 isconnected in series with winding 55 of contactor UV. Winding 55 thenbecomes deenergized to restore contactor UV and open its contact UV1which disconnects the power from the entire control circuit. All of thecontactor-s and timing contactors in the control circuit are thusdc-energized and their contacts are restored to their unoperatedcondition. This disconnects the power source from armature 10 by theopening of contacts H1, L1, and M1. Armature 10 remains connected bylimit switch contacts in the dynamic braking circuit of contact 22,resistors R5 and R6, contact DB2, series field 11 and contact 23. Thepower source is also disconnected from winding 24 of the frictionbrakeso its sets to stop and hold the load by the opening of the samecontacts.

As soon as the voltage across resistor R11 has been reduced to a lowvalue, windings 83A and 83B are deenergized and relay XVR restores toreclose its contact XVR1.

a Drum controller 25 then must be moved to the off position to reset thecontrol circuit. As described for the off position, Winding 55 isenergized through contact XVR1 to operate contactor UV and close itscontacts UVI and UV2.

The operator may now lower the load out of the overhoist limit switch 19by moving drum controller 25 to any of the lowering positions, Lathrough Le, it being preferred that lowering point La be used.

The motor is now energized by current flowing from wire 12 throughcontact L1, armature 10, contact 21, series field 11, to friction brakewinding 24. Current also flows from wire 12 through contact L1, contact20, res'istor R11 to friction brake winding 24. The current then flowsthrough winding 24 and the various resistor sections R1 through R10depending upon the position of drum controller 25. The friction brake isthus released and the motor starts rotating to lower the load.

It is noted that relay XVR is again eneriz'ed by the voltage drop acrossresistor R11, but in this instant the voltage drop is of the reversepolarity. Therefore, current can only flow through winding 83B andcannot flow through winding 83A because of the blocking action ofrectifier 85.

Should the lowering speed of the load become too great, the voltage dropacross resistor R11 would reach the value at which Winding 83B willalone operate relay XVR. Relay XVR will operate to stop further downwardmovement of the load by deenergizing the control circuit and setting thefriction brake in the same manner as previously described.

Thus, it is seen that relay XVR not only prevents the objectionalcycling of the load in and out of the overhoist limit switch, but alsoprevents the load from being lowered too fast out of the limit switch,and provides this function at two different sensitivities.

As" the load is lowered through the overhoist limit switch, contacts 20and 21 re-open and contacts 22 and 23 reclose. This connects the motoras a shunt motor for normal lowering. The reconnection of the motor bythe contacts of the overhoist limit switch could, if the load were beinglowered at a very fast speed, cause a terrific jar to the crane and tothe load itself.

It is seen that relay XVR is connected across series field 11 andcontact 23 during the normal hoisting and lowering operation of thehoist. Therefore, it is sensitive to any excessively high voltageconditions that may exist across the series field. However, in theseinstances only winding 833 will be energized as winding 83A cannot bebecause of the blocking action of rectifier 85. This makes relay XVRquite insensitive to normal transient condi tion and yet allows it tooperate when the overhoist limit switch is tripped at very low voltages.

It is to be noted that when the load was hoisted through overhoist limitswitch 19 in the hoisting direction, both windings were energized tooperate relay XVR. When lowering the load out of the limit switch andafter it has been reset, and when hoisting before tripping the limitswitch only winding 83B was energized. Therefore, it is obvious that inthe former case a much smaller voltage will operate relay XVR than wouldbe required in the latter case. It therefore may be said that relay XVRis polarized to the hoisting direction of operation and nonpolarized tothe other operating conditions.

It has been found that the operation of the circuit is improved and manysafety features are added when the relay XVR is of the time delay typeas described in the co-pending application of Harry M. Cook andChristian Chermely filed on July 10, 1961, hearing Serial Number 122,817and having the same assignee as the instant application. FIGURE 2illustrates the manner in which the relay of that application may beconnected so that it may be polarized to provide the same advantages setforth in this application.

FIGURE 2 shows an XVR relay having a single wind ing 83. Connected inseries with it is a parallel connected resistor 87 and a rectifier 86.Rectifier 86 is poled so it only connects current when dynamic brakingcurrent is flowing in the dynamic braking circuit. In all otherinstances, the current will flow in the reverse direction throughwinding 83 and because of the blocking action of rectifier 86, it mustflow through resistor 87. Therefore, a. high voltage is required tooperate relay XVR when the energizing current flows through the resistorthan when the energizing current flows through rectifier 86 because ofthe voltage drop across resistor 87. Thus, it may be stated that relayXVR is polarized to the one condition and non-polarized to the othercondition.

Although I have described my invention with a certain degree ofparticularity, it is understood that the above disclosure has been madeonly by way of example, as is required by law, and that many changes inthe arrangement of the circuit may be resorted to without departing fromthe spirit and the scope of my invention as hereinafter claimed.

I claim as my invention:

1. In a control system for hoists and the like having a driving motorprovided with a series field; a brake for said motor having an operatingwinding in series with said motor; a reversing type drum controllerconnected in a series circuit to a source by normally closed contacts ofa relay, and having operable contacts and circuits controlled therebyfor selectively connecting said motor to a source for rotation in eitherdirection; a limit switch mechanism having normally closed contacts inthe connections from the motor to the source and normally open contacts;a dynamic braking circuit including a resistor having the normally openlimit switch contacts in the said circuit connections to the armatureand the series field; a relay for operating said normally closed relaycontacts and connected to be energized by the voltage drop across saidresistor when the normally open limit switch contacts are closed and bythe voltage drop across said series field when the normally closed limitswitch contacts are closed; said relay capable of being energized in apolarized manner and responsive to a selected voltage when energized bythe voltage drop across the resistor and in a non-polarized manner andresponsive to selected greater voltage when energized by the voltagedrop across the field; said limit switch responsive to a predeterminedlimit of operation of the motor in one direction for opening thenormally closed limit switch contacts to disconnect the motor from thesource and for closing said normally open limit switch contacts tocomplete the dynamic braking circuit whereby said relay is energized inthe polarized manner by the voltage drop across said resistor and itoperates to open said normally closed contacts which disconnects thedrum controller from the source to deenergize the brake winding, and thebrake sets to assist in stopping and to hold the load.

2. In a control system for hoists and the like as described in claim 1wherein said relay has two energizing windings connected in parallel, arectifier connected in series with one of said windings and in adirection whereby said winding can only be energized by the voltage dropacross said resistor when dynamic braking current is flowing throughsaid resistor.

3. In a control system for hoists and the like as described in claim 1wherein a parallel connected resistor and rectifier are connected inseries with the energizing winding for said relay, and said rectifierconnected in a manner to allow current to flow therethrough to energizesaid winding of said relay only when dynamic braking current is flowingthrough said resistor.

4. In a control system for hoists and the like having a driving motorprovided with a series field; a brake for said motor having an operatingwinding in series with said motor; a reversing type drum controllerconnected to a source by a normally closed contact of a relay and havingoperable contacts and circuits controlled thereby for selectivelyconnecting said motor to a source for rotation in either direction; alimit switch mechanism having normally closed contacts in theconnections from the motor to the source and normally open contacts; adynamic braking circuit including a resistor and having the normallyopen limit switch contacts in the connections to the armature and theseries field; a relay for operating said normally closed contacts andconnected to be energized by the voltage drop across said resistor whenthe normally open limit switch contacts are closed and by the voltagedrop across said series field when the normally closed limit switchcontacts are closed; said relay capable of being energized in apolarized manner and in a nonpolarized manner; said limit switchresponsive to a predetermined limit of operation of the motor in onedirection for opening the normally closed limit switch contacts anddisconnecting the motor from the source, and for closing said normallyopen limit switch contacts to complete the dynamic braking circuit;control circuits responsive to operation of said drum controller forconnecting said motor to said source for rotation in the reversedirection; and should the speed of said motor in the reverse directionbecome too fast, said relay is energized in a non-polarized manner bythe voltage drop across said series field and it operates to open saidnormally closed contact which disconnects the drum controller from thesource to de-energize the brake winding, and the brake sets to stop andhold the motor.

5. In a control system for hoists and the like as described in claim 1wherein additional control circuits are responsive to operation of thedrum controller for connecting said motor to said source for rotation inthe reverse direction after said limit switch has been tripped, wherebyshould the speed of the motor in the reverse direction become too greatbefore resetting said limit switch in the reverse direction, said relayis energized in a non-polarized manner by the voltage drop across saidresistor and said relay operates to open the normally closed contactswhich disconnect the drum controller from the source to de-energize themotor and the brake, and the brake sets to stop and hold the motor.

6. In a control system for hoists and the like having a driving motorprovided with a series field; a brake for said motor having an operatingwinding in series with said motor; a reversing type drum controllerconnected to a source by normally closed contacts of a relay, and havingoperable contacts and circuits controlled thereby for selectivelyconnecting said motor to a source for rotation in either direction; alimit switch mechanism having normally closed contacts in the connectionfrom the motor to the source and normally open contacts; a dynamicbraking circuit including a resistor and having the normally open limitswitch contacts in the said circuit connections to the armature and theseries field; said limit switch responsive at a predetermined limit ofoperation of the motor in one direction for opening the normally closedlimit switch contacts to disconnect the motor from the source and forclosing said normally open limit switch contacts to complete the dynamicbraking circuit; a relay for operating said normally closed contacts andcapable of being energized in a polarized and non-polarized manner, saidrelay connected to be energized in the nonpolarized manner by thevoltage drop across said series field when said limit switch is in itsnormal unoperated condition and only connected to be energized in thepolarized manner by the voltage drop across said resistor due to theflow of dynamic braking current immediately after said limit switch hasbeen operated.

7. In a control system for hoists and the like as described in claim 6wherein additional circuits are responsive to the operation of the drumcontroller for connecting said motor to said source for rotation in thereverse direction after said limit switch has been operated whereby saidrelay is energized by the voltage drop across said resistor in thenon-polarized manner, and after said limit switch has been reset to itsnormal unoperated condition said relay is energized by the voltage dropacross said series field in the non-polarized manner.

8. In a control system for hoists and the like as described in claim 7wherein said relay has two energizing windings connected in parallel, arectifier connected in series with one of said windings and in adirection to allow the flow of current therethrough when dynamic brakingcurrent is flowing through said resistor.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A CONTROL SYSTEM FOR HOISTS AND THE LIKE HAVING A DRIVING MOTORPROVIDED WITH A SERIES FIELD; A BRAKE FOR SAID MOTOR HAVING AN OPERATINGWINDING IN SERIES WITH SAID MOTOR; A REVERSING TYPE DRUM CONTROLLERCONNECTED IN A SERIES CIRCUIT TO A SOURCE BY NORMALLY CLOSED CONTACTS OFA RELAY, AND HAVING OPERABLE CONTACTS AND CIRCUITS CONTROLLED THEREBYFOR SELECTIVELY CONNECTING SAID MOTOR TO A SOURCE FOR ROTATION IN EITHERDIRECTION; A LIMIT SWITCH MECHANISM HAVING NORMALLY CLOSED CONTACTS INTHE CONNECTIONS FROM THE MOTOR TO THE SOURCE AND NORMALLY OPEN CONTACTS;A DYNAMIC BRAKING CIRCUIT INCLUDING A RESISTOR HAVING THE NORMALLY OPENLIMIT SWITCH CONTACTS IN THE SAID CIRCUIT CONNECTIONS TO THE ARMATUREAND THE SERIES FIELD; A RELAY FOR OPERATING SAID NORMALLY CLOSED RELAYCONTACTS AND CONNECTED TO BE ENERGIZED BY THE VOLTAGE DROP ACROSS SAIDRESISTOR WHEN THE NORMALLY OPEN LIMIT SWITCH CONTACTS ARE CLOSED AND BYTHE VOLTAGE DROP ACROSS SAID SERIES FIELD WHEN THE NORMALLY CLOSED LIMITSWITCH CONTACTS ARE CLOSED; SAID RELAY CAPABLE OF BEING ENERGIZED IN APOLARIZED MANNER AND RESPONSIVE TO A SELECTED VOLTAGE WHEN ENERGIZED BYTHE VOLTAGE DROP ACROSS THE RESISTOR AND IN A NON-POLARIZED MANNER ANDRESPONSIVE TO SELECTED GREATER VOLTAGE WHEN ENERGIZED BY THE VOLTAGEDROP ACROSS THE FIELD; SAID LIMIT SWITCH RESPONSIVE TO A PREDETERMINEDLIMIT OF OPERATION OF THE MOTOR IN ONE DIRECTION FOR OPENING THENORMALLY CLOSED LIMIT SWITCH CONTACTS TO DISCONNECT THE MOTOR FROM THESOURCE AND FOR CLOSING SAID NORMALLY OPEN LIMIT SWITCH CONTACTS TOCOMPLETE THE DYNAMIC BRAKING CIRCUIT WHEREBY SAID RELAY IS ENERGIZED INTHE POLARIZED MANNER BY THE VOLTAGE DROP ACROSS SAID RESISTOR AND ITOPERATES TO OPEN SAID NORMALLY CLOSED CONTACTS WHICH DISCONNECTS THEDRUM CONTROLLER FROM THE SOURCE TO DEENERGIZE THE BRAKE WINDING, AND THEBRAKE SETS TO ASSIST IN STOPPING AND TO HOLD THE LOAD.